Allotropes of iron

Common card · No. 268789

At atmospheric pressure, three allotropic forms of iron exist, depending on temperature: alpha iron (α-Fe, ferrite), gamma iron (γ-Fe, austenite), and delta iron (δ-Fe, similar to alpha iron). At very high pressure, a fourth form exists, epsilon iron (ε-Fe, hexaferrum). Some controversial experimental evidence suggests the existence of a fifth form that is stable at very high pressures and temperatures. The phases of iron at atmospheric pressure are important because of the differences in solubility of carbon, forming different types of steel. The high-pressure phases of iron are important as models for the solid parts of planetary cores. The inner core of the Earth is generally assumed to consist essentially of a crystalline iron-nickel alloy with ε structure. The outer core surrounding the solid inner core is believed to be composed of liquid iron mixed with nickel and trace amounts of lighter elements.

Read on Wikipedia · Image Diagramma_di_fase_del_ferro_puro.svg: Daniele Pugliesi derivative work: Daniele Pugliesi (talk), CC BY-SA 3.0